# US 4,395,090 A · Optical cut-off filter

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 4,395,090 A
- Document ID: US4395090A
- Status: Granted
- Kind: A
- Application number: 06/240,868
- Filed: 1981-03-05
- Granted: 1983-07-26
- Earliest claimed: 1980-03-25
- Assignees: Siemens Aktiengesellschaft
- Inventors: Hans F. Mahlein
- Web page: https://patentgrep.com/patent/US4395090A

## CPC

- G02B 5/282: {reflecting for infrared and transparent for visible light, e.g. heat reflectors, laser protection}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

An optical cut-off filter characterized by a multi-layer system comprising of a sequence of dielectric layers which are bordered on each side by a transparent medium having an equal or same index of refraction with the index of refraction of each of the dielectric layers being selected so that for a preselected radiation angle of incidence, the band paths of the filter have an envelope of reflected secondary maximum for a component vibrating perpendicular to the radiation plane of incidence and the envelope for a component vibrating parallel to the radiation of planar incidence of the electrical field vector of incident radiation, and both envelopes exhibit zero locations which have a different wavelength due to the selection of the index of refraction of the dielectric layers forming the filter.

## Claims

### Claim 1

In an optical cut-off filter in the form of a multilayer system comprising a sequence of dielectric layers A and B interposed between a transparent bordering medium having an index of refraction n.sub.0, and with an index of refraction n.sub.A for each of the layers A and an index of refraction n.sub.B for each of said layers B selected so that, for a preselected radiation angle of incidence .theta., the pass band of the filter has an envelope E.sub.s of the reflecting secondary maxima for the s-component vibrating perpendicular to the radiation plane of incidence and an envelope E.sub.p for the p-component vibrating parallel to the radiation plane of incidence of the electrical field vector of the incident radiation, and wherein each envelope has a zero location, the improvement comprising having the indices of refraction n.sub.A and n.sub.B of the dielectric layers A and B of the filter selected so that the zero locations of the two envelopes E.sub.s and E.sub.p lie at somewhat different wavelengths.

### Claim 2 (depends on 1)

The optical cut-off filter according to claim 1, wherein the multi-system layer exhibits a layer structure ##EQU32## wherein ##EQU33## signifies k multiple sequences of symmetrical layers A and B layers of a fundamental period of ##EQU34## wherein the layer A/2 has the index of refraction n.sub.A and the layer B has the index of refraction n.sub.B and S signifies the bordering transparent medium having an index of refraction n.sub.0.

### Claim 3 (depends on 2)

The optical cut-off filter according to claim 2, wherein n.sub.0 =1.46, n.sub.A =2.35, n.sub.B =1.70 and k=13.

### Claim 4 (depends on 2)

The optical cut-off filter according to claim 2, wherein n.sub.0 =1.46, n.sub.A =2.35, n.sub.B =1.90 and k=18.

### Claim 5 (depends on 2)

The optical cut-off filter according to claim 2, wherein n.sub.0 =1.46, n.sub.A =2.35, n.sub.B =1.65 and k=13.

### Claim 6 (depends on 2)

The optical cut-off filter according to claim 2, wherein n.sub.A >n.sub.B.

### Claim 7 (depends on 2)

The optical cut-off filter according to claim 2, wherein the indices of refraction n.sub.A and n.sub.B are greater than the index of refraction n.sub.0 of the transparent medium S.

### Claim 8 (depends on 7)

The optical cut-off filter according to claim 7, wherein n.sub.A >n.sub.B.

### Claim 9 (depends on 7)

The optical cut-off filter according to claim 7, wherein the radiation angle of incidence .theta. is at .theta.=45.degree. and the indices of refraction n.sub.B, n.sub.A and n.sub.0 satisfy the following relationship: ##EQU35##

### Claim 10 (depends on 9)

The optical cut-off filter according to claim 9, wherein n.sub.A >n.sub.B.